In cohort studies comparing disease incidence between two groups, which statistical term is appropriate?

• A. Relative risk
• B. Odds ratio
• C. Hazard ratio
• D. Risk difference

Answer: (A)

In cohort studies that compare disease incidence between two groups, relative risk is the appropriate statistic because it directly compares the probability of developing the disease in the exposed group to the probability in the unexposed group. This ratio of cumulative incidences shows how much more (or less) likely the outcome is with exposure and is easy to interpret—if the relative risk is 2, the exposed group has twice the risk. The odds ratio is more aligned with case-control designs and can mislead when the outcome is common. The hazard ratio comes from time-to-event analysis and accounts for when events occur and censoring, rather than just overall incidence. The risk difference gives an absolute gap in risk between groups, which is informative for public health impact but doesn’t express the strength of association as clearly as a relative measure. So, for comparing incidence between two cohorts, relative risk is the most straightforward and appropriate choice.